1. Field of the Invention
The present invention relates to a vibration actuator, a lens barrel and a camera.
2. Related Art
A vibration actuator includes an elastic member and a relative movement member. The elastic member generates oscillatory waves by oscillation of an electromechanical conversion element. The relative movement member with which the elastic member is in pressure contact is driven by the oscillatory waves to rotationally move with respect to the elastic member. A vibration actuator has been conventionally known in which a porous plastic material is used for a contacting surface of an elastic member or a relative movement member. Pores of the porous plastic material are filled with a lubricant for improved lubricating ability (for example, Japanese Patent Application No. S62-173227).
However, contact points at the contacting surface between the elastic member and the relative movement member differ depending on ambient temperature. More specifically, at a low temperature, the elastic member contracts and deforms such that an inner peripheral side of the elastic member departs away from and an outer peripheral side approaches a driven face of the relative movement member. On the other hand, at a high temperature, the elastic member expands and deforms such that the inner peripheral side of the elastic member approaches and the outer peripheral side departs away from the driven face of the relative movement member. As a result, even if the lubrication performance of the vibration actuator is improved by the pores filled with the lubricant, there is a problem of variation in the driving performance depending on the ambient temperature at which the vibration actuator is used.